SPRINGFIELD - A defense lawyer for Jesus Gilberto Garcia, accused of killing his ex-girlfriend's mother in 2010, asked jurors in an ongoing trial in Hampden Superior Court to acquit his client of first-degree murder in order to honor the victim's fierce maternal instincts.

It was an unusual argument in an unusual defense on behalf of Garcia, 20, of Springfield, charged with fatally stabbing Valerie Girouard, 47 of Hampden, on July 30, 2010, and seriously wounding her live-in boyfriend during the same incident.

Undisputed testimony in the case showed the attacks happened after Girouard's 15-year-old daughter rebuffed Garcia following a tumultuous, long-term courtship. Garcia returned to the tiny house at 90 Main St. nine days after breaking in once before and holding a knife to Mariah Girouard's neck "to teach her the world wasn't safe," the teen girl testified at trial.

The first incident prompted Valerie Girouard to vow that Garcia "would have to go through her first" if he tried to get to her daughter again, Mariah Girouard told jurors. And, defense lawyer Paul Rudoff told the panel on Monday that is precisely how the attacks played out.

"Valerie Girouard was determined to do everything in her power to protect her daughter ... doesn't it make sense to you that she would pick up that kitchen knife?" Rudoff asked jurors, adding that his client only wanted to see Mariah Girouard and didn't intend to hurt anyone.

He asked jurors to find Garcia of lesser counts of which he is clearly guilty, but to acquit his client on the most serious charge of first-degree murder to "accurately represent the full extent of those heroic efforts that (Valerie Girouard) made," when she attacked Garcia to protect her daughter.

However, Assistant District Attorney James Forsyth countered that Garcia rode a borrowed bicycle 7.5 miles to the Girouard's home because he intended to rape Mariah Girouard and "finish what he started" during the previous assault, when he stopped short of doing any serious harm.

Distance and locked doors were no obstacle for Garcia, Forsyth argued.

"Only one obstacle left: Valerie," the prosecutor said.

After four days of prosecution witnesses, the defense put on just one: Dr. Bruce Bartholow, a professor of psychology at the University of Missouri and an expert in the potential effects of video game violence on adolescent males.

The theory has rarely been raised as a defense in a criminal case, and is even more infrequently allowed as testimony. Judge Mary Lou Rup allowed Bartholow to testify after discussing the legitimacy of his laboratory studies in court on Monday morning.

While on the witness stand, he told jurors that repeated studies of brain waves in young males with a history of playing violent video games as many as 40 hours per week desensitized many of them to violent imagery and made them more prone to behave aggressively.

Several witnesses testified Garcia and his nephews often engaged in marathon video game sessions, playing at being killer Ninjas and other characters for days on end.

Jurors were expected to begin deliberations in the case on Monday afternoon.